Shackle assemblies are elements used for connecting chains or wires in various load applications. Typically, a shackle assembly or shackle has a set of shackle arms which are connected to each other at one end by a bridge portion, so that a substantially U-shaped shackle body is obtained, which is open at the end opposite to the bridge portion. This shackle body can be closed with a shackle pin, which is typically received in openings in the shackle arms. One of the openings as well as one end of the shackle pin can be provided with a thread, so as to hold the shackle pin in its position, when threaded into the shackle body.
Shackles are used in situations where large loads or pulling forces are applied to ropes, chains, etc. For safety reasons, it is of great benefit to provide a load measuring function to the shackle assembly to monitor the applied loads, and to stop loading/pulling if the forces applied to the shackle assembly exceed a maximum load which has been set as a safety value.
One known shackle assembly (an off-the-shelf-product) is provided with a strain gauge attached to the shackle body, at portions which exhibit the most bending deformation when the load is applied. The load applied to the shackle assembly can be derived from the strain gauge signals. In practice, the strain gauge is applied to the outer surface of the shackle body. A plastic cover is provided to protect the strain gauge against ambient conditions and shocks.
The inventors have found that with standard parts, the accuracy of the measurement of the forces applied to the shackle assembly can be less than desirable. Additionally, the known shackle assembly suffers from the problem that the strain gauge is easily damaged, requiring exchange of the shackle assembly.